First, a high-energy thioester bond is formed between ubiąuitin (Ub) and a ubiquitin-activating enzyme (El). This reaction requires ATP hydrolysis. Secondly, the activated ubiquitin is transferred to a ubiquitin conjugating enzyme (E2). Thirdly, the activated ubiquitin is ligated to the protein substrate by a ubiquitin ligase (E3). Lastly, the ubiquitin chain is elongated by an ubiquitin-chain elongating factor (E4), which drives the assembly of the polyubiquitin chain.
From: Assembly of Protein Aggregates in Neurodegeneration: Mechanisms Linking the L'biquitin/Proteasome Pathway and Cha peron es
Protein
ATP
Ub
% 3
E2
Conjugation
Ub
Ligatfion
Elongation